Awesome list, Zombie! I'd like to add that some forms of same-sex marriage have been allowed throughout history on a technicality. In the Middle Ages, for instance, the church technically recognised marriage between a man and a eunuch.
Also, some Native American tribes have recognised same-sex unions through the concept of people with two souls, technically a form of transsexuality, where a person of one sex could take on the gender roles of the opposite sex, to the point of marrying a person of the same physical sex as themselves.
Out of curiosity, is there anywhere on these forums where one is permitted to discuss politics?